Your immune system is a complicated network of specialized cells, organs, and tissues that communicate with each other and work together to recognize and attack foreign invaders.

These invaders could be germs such as viruses, bacteria, or fungi. When an invader gets into your body, your immune system uses your lymphatic system and your circulatory system to bring specialized white blood cells to the site of the invasion (one white blood cell is shown at left amid red blood cells).

Your immune system then produces antibodies or special chemicals that attach to the invader to inactivate or destroy it. Some parts of the immune system include the thymus, which produces T cells that protect the body from infection; the spleen, which filters the blood and clears it of bacteria and viruses; and bone marrow, which produces new red and white blood cells.

Immune System Conditions

Problems can occur when your immune system is underactive or overactive. Some children are born with underactive immune systems, which can lead to life threatening infections.

An infection with HIV, the virus that causes AIDS, can also result in not having enough immunity. Examples of an overactive immune system include allergic reactions and autoimmune diseases.